Sells, 49, was convicted of murdering 13-year-old Kaylene Harris, the daughter of an acquaintance, in 1999.

Armed with a butcher knife, he tried to molest the sleeping Kaylene and then stabbed her 16 times — slitting her throat several times — when she tried to escape. He then slit the throat of a friend who was sleeping in the top bunk before fleeing. She survived.

Texas Department of Criminal Justice

Tommy Sells

Sells subsequently claimed to have committed as many as 70 murders during two decades as a drifter, though authorities have not corroborated those claims.

Sells made no last statement, Texas officials said.

He was pronounced dead at 6:27 p.m. local time (7:27 p.m. ET), about 13 minutes after the pentobarbital was injected.

According to The Associated Press, as the drug made its way through the inmate's bloodstream, Sells took a few breaths, before his eyes closed and he began to snore. He stopped moving after less than a minute.

Kaylene Harris' father, who witnessed the execution, told the AP the injection was "way more gentle than what he gave out."